1. Field of Invention
This invention relates to improvements in a lock-up clutch provided in a torque converter used in an automobile and, more particularly, relates to a damper mechanism in a clutch mechanism.
2. Description of the Related Art
A torque converter of the type having a lock-up clutch is provided between an engine and an automatic transmission in order to improve fuel efficiency of the vehicle in which it is utilized.
The conventional lock-up clutch type torque converter is hereinafter described according to FIG. 3 which is an axially cross-sectional view of the lock-up clutch type torque converter.
Referring to FIG. 3, a lock-up clutch type torque converter comprises a torque converter mechanism 12, including a pump 8 which is connected for rotation with an input shaft 7 for transmitting rotational torque to a turbine 9 which is connected for rotation with an output shaft 10. A clutch mechanism is indicated at 14. The clutch mechanism 14 includes a front cover 1 which is connected to the input shaft 7 at an inner periphery thereof, a lock-up piston 2 which is disposed between the front cover 1 and the torque converter mechanism 12. The piston 2 is mounted on the input shaft 7 so as to be axially movable and engage or disengage with the front cover 1 via a frictional member 22. Movement of the piston is controlled by oil pressure supplied into a space defined by the front cover 1 and the lock-up piston 2. An annular disk 3 is arranged between the lock-up piston 2 and the torque converter mechanism 12 and has a plurality of concave portions 31 (FIG. 5) formed on the outer periphery at equally spaced intervals which are engaged with an axially extending projection 21 at the outer periphery of the lock-up piston 2. A plate member 4 is provided at both sides of the annular disk 3 and is elastically connected to the annular disk 3 by a plurality of elastic members 5, 61, 62. The plate member 4 is defined by a main plate 41 and a sub plate 42 connected with each other by a pin 43.
FIG. 4 illustrates a partial enlarged view of the clutch mechanism 14 of FIG. 3. FIG. 5 illustrates a plane view of damper of the clutch mechanism 14 of FIG. 4. Referring to FIG. 4 and FIG. 5, the annular disk 3 is rotatable with respect to the main plate 41 and the sub plate 42 and is elastically connected thereto by the coil spring 5. The coil spring 5 is compressed by the annular disk 3, the main plate 41 and the sub plate 42 in a first compression stage at the time rotational torque is input from the engine (not shown).
The coil springs 61 and 62 are disposed radially inwardly of the coil spring 5. A predetermined rotational angle ".alpha." is provided between the coil spring 61 or 62 and the annular disk 3. The coil springs 61 and 62 are compressed by rotation of the annular disk 3 through an angle greater than the predetermined rotational angle ".alpha.".
In the second stage of compression, the annular disk 3 has a flange 32 which extends radially inwardly. The flange 32 presses against the coil spring 61 only after movement through a predetermined rotational angle ".beta.". The flange 32 contacts to an open end 4b of an opening 4a in a space 4d which receives the coil spring 61. In a third compression stage, the annular disk 3 rotates through an angle greater than the rotational angle ".alpha.+.beta.," and the annular disk 3 rotates together with the plate member 4 by the flange 32 and the open end 4b of the opening 4a.
Another conventional lock-up clutch torque converter is illustrated in FIG. 6. A stopper portion of the damper structure of the clutch mechanism has a cut-away portion 33 which is formed in the annular disk 3. A stopper pin 44 connects the main plate 4 and the sub plate 42 with each other. The annular disk 3 and the plate member 4 rotate with each other after a predetermined rotation of the stopper pin 44 through the cut-away 33. Both ends of the stopper pin 44 are connected to the plate member 4.
The stopper in the foregoing conventional clutches is required to have great strength because the torque acting on the stopper is generally extremely large. Therefore, the problem in the clutch mechanisms illustrated by FIG. 4 and FIG. 5 is the size in the radial direction of the flange 32 as the stopper has to be as large as possible so as to provide a stopper of sufficient strength.
The stopper illustrated in FIG. 6, is required to have increased hardness of the stopper pin 44 in order to increase the strength thereof. However, the hardness of the ends of the stopper pin 44 is required to be decreased in order to permit a rivet connection at the ends of the pin. Accordingly, there is difficulty in the production of the device due to the changing of the hardness of the stopper pin 44 in a unitary body. Moreover, the number of parts is increased by providing the stopper in addition to the springs 61 and 62.